1. Technical Field
The present invention relates to an emulsifier containing a sphingoglycolipid having a specific structure. Because the emulsifier of the present invention has excellent moisturizing effect, skin roughening preventing effect, and emulsifying effect, it can widely be used for cosmetic and medical products. Moreover, the present invention also relates to a method for producing an emulsified composition using the emulsifier, and an emulsified composition using the emulsifier.
2. Description of Related Art
Skin roughening is caused by loss of too much moisture from skin surface, when air is dry, skin is washed or the like. Further, since various chemicals have overflowed in the society in these days, the functions of the skin having touched these chemicals are likely to be deteriorated, and thus the skin roughening state is often caused by decrease of the lipid secretion function or the like. For this reason, it has been desired to provide a composition that can prevent skin roughening in advance and has excellent moisturizing effect.
As active compounds having moisturizing effect, various compounds, mainly water-soluble polyhydric alcohols, have been provided so far. Among those, some are already put into practical use like propylene glycol. However, many of those moisturizing compounds put into practical use are accompanied by unpleasant feeling when they are applied to the skin, or exhibit only insufficient moisturizing effect. Therefore, it is still desired to develop a novel moisturizing compound.
Under such a situation, sphingoglycolipids attract attentions as a safe moisturizing compound.
For example, it is disclosed that sphingoglycolipids have skin moisture retaining effect in Japanese Patent Unexamined Publication (KOKAI) Nos. 1-242690, 2-48520, 4-159203, and Japanese Patent Publication (KOKOKU) No. 6-80007. However, structures or compositions of sphingoglycolipids that are used in the examples of these patent documents are not clarified.
Moreover, Japanese Patent Unexamined Publication (KOKAI) No. 6-157283 discloses a moisturizing cosmetic for skin external application which is characterized by inclusion of a sphingoglycolipid represented by a specific general formula as one of its ingredients. However, the saccharide portion mentioned in the general formula is described simply as a saccharide residue, and it does not refer to the detail of the saccharide portion.
Thus, while it has been known that sphingoglycolipids have moisturizing effect, substantially no research has been made about the chemical structures of the sphingoglycolipids having such moisturizing effect.
As a document that specifically mentions sphingoglycolipids having the moisturizing effect, Japanese Patent Unexamined Publication (KOKAI) No. 61-286307 can be mentioned. This patent document describes that gangliosides have skin moisturizing effect and skin softening effect, and discloses a skin cosmetic containing a ganglioside or a salt thereof. Gangliosides are sphingoglycolipids characterized by inclusion of an aminosaccharide and sialic acid in addition to a neutral saccharide.
Further, Japanese Patent Unexamined Publication (KOKAI) Nos. 5-39485, 7-133217, and 7-285827 disclose agents for skin external application which utilize cerebrosides. Cerebrosides are sphingoglycolipids consisting of fatty acid, sphingosine base, and neutral saccharide (galactose or glucose) in a molar ratio of 1:1:1.
As described above, as for the sphingoglycolipids having the moisturizing effect to the skin, only several kinds of structures have been specified. Therefore, it has not been elucidated at all for what kind of structure of sphingoglycolipids generally impart potential moisturizing effect to them. For this reason, even when a mixture of sphingoglycolipids was obtained from a living organism, the mixture must be used as it was since such a potential active ingredient was unknown, and thus the moisturizing effect could not be properly enhanced by purification. Moreover, because any general structure of sphingoglycolipids having potential activity has not been elucidated, moisturizers have also scarcely been produced by chemical synthesis.
Further, to use as an ingredient of cosmetics and the like, an ingredient must have a property that it can be easily formulated as cosmetics in addition to the moisturizing effect and skin roughening preventing effect. Since many of cosmetics are composed of an emulsified composition of oil component and aqueous component, ease of utilization for an emulsified composition is very important for the ingredient. Therefore, if an active ingredient which also exhibit emulsifying effect in addition to the moisturizing effect or the skin roughening preventing effect can be provided, it will be very useful. However, sphingoglycolipids have never been studied from such a viewpoint so far.
In view of these problems of the prior art, the present inventors conducted studies aiming at identifying structures of sphingoglycolipids having potential moisturizing effect, skin roughening preventing effect, and emulsifying effect. That is, the object of the present invention was to identify a group of sphingoglycolipids having potential moisturizing effect, skin roughening preventing effect, and emulsifying effect, and thereby provide an emulsifier containing them. Further, the present invention also aimed at providing an emulsified composition using such an emulsifier, and an effective method for producing an emulsified composition using such an emulsifier.